A Jersey City woman had an unbreakable smile on her face yesterday as she held onto her granddaughters — Gia, 3, and Laila, 4 — whom she had just officially adopted.

“I feel I had to step up to the plate and take care of them,” said Reina Martinez, who explained that the girls’ mother has an illness and their father hasn’t been in their lives. “I accepted them from day one. I knew that’s what I wanted to do.”

Martinez was one of nine families that finalized adoptions yesterday at the Hudson County Administration Building in Jersey City as part of National Adoption Day.

A total of 15 children were adopted, bringing the total to 79 on the year in Hudson County, officials said.

Bryant Jeffries and his fiancee, Michelle Kelly, drove 13 hours from Jonesboro, Ga., to Jersey City to make another life-long commitment: adopting Jeffries’ grandchildren, 1-year-old Zaniya and 2-year-old Crystal.

“He asked me would I help him raise his grandchildren,” Kelly said. “I said, ‘Not a problem.’ We don’t want them to go into the (foster care) system with a stranger. It’s better for them to be with family.”

Event organizer Lizette Mateo, a Division of Child Protection and Permanency representative, said that the trend in recent years has been family members stepping forward to take care of young relatives.

Vilma Rosario, 51, said she adopted her niece’s two sons because her niece was unable to take care of them. Aunt Vilma is now “mom” to Abraham, 4, and Jordan, 11.

“I feel very great because I get to be with my favorite mom,” Jordan said. “I’m looking forward to having a great life.”

Carmona beamed as Abraham showcased his break-dance moves in the middle of the floor with a face-full of cupcake icing. “He’s a pain sometimes, but I wouldn’t want to live without him.”

The balloon-filled and pastry-packed reception made the new families feel at home.

“It can be difficult and heartbreaking, but this is one day everyone can truly feel excited,” said Beverly Savage, executive director of the Hudson County Court of Appointed Special Advocates, which co-sponsored the event.

The state Department of Child Protection and Permanency, United Way of Hudson, Hudson County Court, Foster and Adoptive Family Services and United Parcel Services were also sponsors.